1. Field of the Invention
This invention relates to, in general, improved semiconductor devices and, more particularly, to packages for high power semiconductor devices having an insulated heat spreader adapted to be thermally coupled to but electrically isolated from an external heat sink.
2. Background Art
Power semiconductor devices must dissipate substantial amounts of heat. To accomplish this they are typically provided with metallic heat spreaders which are adapted to couple directly to an external heat sink. The semiconductor die within the device are usually mounted directly on the heat spreader in order to obtain the most efficient heat transfer to the external heat sink. As a consequence the heat spreader is electrically coupled to the semiconductor die. As used herein, the words "heat spreader" refer to the thermally and electrically conductive member which is the principal heat extraction pathway between the heat source and the external heat sink.
In many applications, the semiconductor die must be at one electrical potential while the external heat sink is at a different electrical potential. In the prior art, two approaches have been taken to provide electrical isolation of the semiconductor chip while still maintaining some degree of thermal coupling to the external heat sink. These are: (1) inserting a thin ceramic isolator between the semiconductor chip and the heat spreader, or (2) placing a thin sheet of mica or plastic between the heat spreader and the external heat sink. The first of these approaches has the disadvantages of, (a) introducing a significant thermal impedance between the semiconductor die and the heat sink at the point of greatest thermal flux, and (b) significantly increasing manufacturing cost. The second approach suffers from the disadvantages that the mica or plastic sheet is, (a) a separate piece part which must be handled during mounting of the finished device to the external heat sink, thereby increasing the overall cost to the user, and (b) generally thicker, for ease of handling, than needed for electrical purposes, thereby increasing the thermal impedance. Thus, a need continues to exist for low cost power semiconductor devices and power semiconductor device packages in which the heat transfer face is electrically isolated from the semiconductor chip without substantial sacrifice in thermal performance, and which does not require the use of external isolators in mounting the device to the external heat sink.
Accordingly, it is an object of the present invention to provide an improved semiconductor power device in which the external heat transfer face is electrically isolated from the semiconductor die.
It is a further object of this invention to provide an improved semiconductor power device in which the external heat transfer face is electrically isolated from the semiconductor chip without the use of a dielectric spacer between the semiconductor chip and the heat spreader.
It is an additional object of this invention to provide an improved semiconductor power device adapted to provide electrical isolation between the semiconductor die and the external heat sink without the use of separate external insulating means.
It is a further object of this invention to provide an improved semiconductor power device in which electrical isolation is achieved by means of an insulating layer which is intimately bonded to the outward, heat transfer, face of the heat spreader.
It is a yet further object of the present invention to provide the above improved device in which the heat transfer face is substantially flat and smooth.
It is an additional object of this invention to provide an improved semiconductor power device which may be constructed with a minimum number of piece parts.
It is a further object of this invention to provide an improved semiconductor device wherein the piece parts are initially substantially flat to promote ease of assembly.
It is an additional object of this invention to provide an improved semiconductor device which is mechanically rugged and well adapted to the industrial environment.
It is a further object of the present invention to provide an improved method for the manufacture of power semiconductor devices and power semiconductor device packages having the above improved features.